各向异性岩应力-渗流耦合问题的反分析

在岩土工程实践中对于诸如各向异性岩体的应力-渗流耦合分析等复杂问题,建立用于同时确定多类参数的反分析方法具有重要意义。以位移量测信息为基础信息,对基于复变量微分法的优化算法（Levenberg-Marquit法）引入异步长因子矩阵 ,建立同时反演确定初始地应力、围岩性态参数和渗透系数的协同优化变步长反演算法。对不同的参数借助搜索迭代过程,确定不同的步长因子系数。异步长因子矩阵可使在峰值附近不收敛的参数重新选择搜索方向,使其收敛至精确值。算例表明,异步长因子矩阵可成功地用于协调各类参数敏感性之间的差异,从而有效改进多参数耦合反演的收敛性和收敛速度,使算法具有更好的适应性和有效性,为岩土工程的复杂问题的求解提供一种方法。     

An extended Cam Clay model for soft anisotropic rocks

The mechanical behaviour of soft sedimentary rocks in triaxial compression is modelled by means of a constitutive law which has been formulated by extending the original Cam Clay model. The geological material is assumed to be linearly elastic-plastic, strain-hardening, with fixed transverse isotropy. Theoretical predictions are compared to observed behaviour at different confining pressures of specimens of diatomite with various bedding inclinations. Although quantitative agreement is not always satisfactory, the trend of the tests is qualitatively well matched, what proves the paradigmatic value of this type of model not only for soils but even for soft rocks.     

Subcritical crack propagation in rocks: theory,experimental results and applications

The micromechanisms of tensile fracture are reviewed, with particular emphasis on the influence of chemical effects on fracture controlled by pre-existing cracks (stress corrosion). A fracture mechanism map for quartz is presented which was constructed using a combination of theoretical insights and experimental data. The manner in which stress corrosion will modify the predictions of fracture mechanism maps is discussed by reviewing the numerous theories of stress corrosion. Experimental data are presented on stress corrosion in tensile deformation of quartz, quartz rocks, calcite rocks, basaltic rocks, granitic rocks and other geological materials. Although the experimental evidence for stress corrosion is overwhelming, very few data were obtained under conditions that simulate those in the bulk of the earth's crust and so the extent of its geophysical significance is yet to be fully established. Examples are given, however, of how invoking stress corrosion as a rate-controlling deformation mechanism sheds new light on extremely diverse geophysical phenomena, such as: predicting the strength and sliding friction properties of rocks, modelling earthquake rupture, the stability of hot, dry-rock geothermal reservoirs, stimulation of oil and gas reservoirs, the crack-seal mechanism of rock deformation and low stress dilatancy, fracture mechanics of lunar rocks, magmatic intrusions and the relaxation of internal stresses in rock.     

A discrete approach for anisotropic plasticity and damage in semi-brittle rocks

In this paper, we propose an anisotropic plastic damage model for semi-brittle geomaterials based on a discrete thermodynamic approach. The macroscopic plastic deformation is generated by frictional sliding of weakness planes. The evolution of damage is related to growth of such weakness planes. The local frictional sliding in each family of weakness planes is described by a non-associated plastic model taking into account material softening and volumetric dilatancy. The damage evolution is coupled with plastic deformation and modelled by an isotropic damage criterion. The proposed model is applied to modelling mechanical responses of typical sandstone under different loading paths. There is good agreement between numerical predictions and experimental data. Further, the anisotropic distributions of plastic deformation and induced damage are analysed and discussed.     

一种确定各向异性单轴抗压强度的经验公式

岩石的单轴抗压强度可以通过相对简单且经济的方法直接测试得到,在岩土工程领域应用十分广泛。提出了一种确定岩石各向异性单轴抗压强度的经验公式。通过该经验公式对砂岩、千枚岩、板岩和页岩的各向异性单轴抗压强度数据进行了拟合。采用决定系数R~2、相对误差D_p和平均绝对相对误差AAREP这3种统计参数评价经验式的预测能力,结果表明,预测的单轴抗压强度与试验值吻合较好。基于包含274个各向异性单轴抗压强度的数据库,通过统计分析评价了经验公式的预测能力,并与3种常用方法的预测能力进行了对比。统计分析表明,仅有3个方位角(β分别为0°、30°和90°)的试验数据可用时,提出的经验式也能够很好地预测各向异性单轴抗压强度。     

Innovation of experimental methodology for adsorbed gases on hydrocarbon-source rocks

As compared to the device developed by our predecessors, the newly developed adsorbed gas degasification-collection device has a series of advantages such as wide sample application range, large sample inlet, high vacuum, short-time sample smashing, low crushing temperature and water-free gas collection, which ensure the geochemical characteristics of acquired adsorbed gas samples to be the same as those of the adsorbed gases on corresponding hydrocarbon-source rocks. The results showed that the acquired adsorbed gases are composed mainly of hydrocarbon gas and carbon dioxide gas, with the hydrocarbon gas accounting for more than 80%, and can be measured reliably for their δ13C1-δ13C3 data, even δ13C4-δ13C5 data. The results of carbon isotope test and analysis satisfy the needs for the geochemical study and application of adsorbed gases. The above new techniques of experimental geochemistry are helpful for establishing the new direct natural gas-source correlation method, proving that the previous usual method of indirect natural gas-source correlation is scientific and authentic, thus providing the experimental basis for the study and application of adsorbed gases on hydrocarbon-source rocks.     

岩石疲劳强度试验和弹性理论分析初步研究

通过单轴压缩试验研究了岩石强度,并用空间弹性力学理论进行分析比较,采用高频振动疲劳试验研究了岩石的疲劳强度,得出了试验中所用材料603号花岗岩的纵向应力-应变曲线以及疲劳强度区间,并对其疲劳现象进行了分析。     

软岩饱水软化过程微观结构演化的临界判据

针对红层软岩遇水软化问题,在已开展的粉砂质泥岩饱水软化试验结果的基础上,从建立软岩微观结构模型出发,定量化研究软岩软化的力学机制。首先将描述粉砂质颗粒特性的结构元件引入到M. Tuller、D. Or提出的黏土矿物微结构模型中,提出了软岩微观结构组合元件;然后结合软岩饱水软化试验中微观结构测试结果,考虑天然状态软岩微观结构的基本类型特征,建立了描述粒状结构与致密条块状结构软岩的两类典型微观结构单元;在此基础上,采用重整化群方法,分别建立了两类软岩软化的重整化模型,并基于重整化原理,分析了软岩软化过程微观结构演化的临界判据,搭建了软岩微观结构与其力学特性之间的定量关系。通过对比软岩饱水软化过程力学性质试验结果,验证了所建立模型的合理性,为进一步开展软岩软化全过程定量化研究奠定基础。     

Scaling laws for hydraulic fractures driven by a power-law fluid in homogeneous anisotropic rocks

This study investigates parametric space of solutions for a planar hydraulic fracture propagating in a homogeneous anisotropic rock. It is assumed that the fracture has an elliptical shape and is driven by a power-law fluid. The purpose of this study is to investigate the influence of anisotropy and power-law fluid rheology on the parametric space of solutions. Rock anisotropy is represented by having two values of fracture toughness, one in the vertical direction and another one in the horizontal direction. Similarly, the effect of elastic anisotropy is approximated by using two different effective elastic moduli in the vertical and horizontal directions. In contrast to the isotropic case, for which there are four limiting solutions, the problem for anisotropic rocks features six different limiting cases. These cases represent competition between toughness and viscosity in the vertical and horizontal directions and competition between fluid storage inside the fracture and fluid leak-off into formation. Approximate expressions for the limiting solutions are obtained using global volume balance and tip asymptotic solutions. Despite the developed solutions rely on a series of approximations, they precisely capture all the scaling laws associated with the problem. Zones of applicability of these limiting solutions are calculated, and their dependence on the problem parameters is investigated.     

Orthopyroxene-magnetite-quartz oxygen barometer for Mnbearing rocks (experimental calibration)

The compositions of orthopyroxene, associated with magnetite and quartz in the system FeO-MgO-MnO-SiO₂ were determined experimentally at temperatures of 700, 750, 800°C and pressures ranging between 3 and 5 kbar. On the basis of data obtained the value of the Guggenheim parameter of orthopyroxene solid solution was calculated: A_{Fe. Mn} = 2400 ±500 cal. For rocks rich in MnO, a modified version of orthopyroxene-magnetite-quartz oxygen barometer is suggested.     

岩体冻融过程中水热耦合非线性分析

针对工程地质和岩土工程中所涉及到的冻害问题,在质能平衡的基础上,充分考虑冻结岩体的热传导、水和岩体存在的热交换以及水热梯度共同作用下水分的迁移与转化,建立了水热耦合的非线性控制方程;对寒区大阪山隧道围岩的温度场和水分场进行数值模拟,并分析其水热耦合迁移规律.模拟结果表明:隧道围岩水分受冻结抽吸力和温度梯度的作用发生迁移,在隧道边墙处渗流速度最大;在考虑水分场时,隧道围岩的冻结圈将变薄,而且随着水分场中渗流系数的增大将更加变薄,水分场在很大程度上影响温度场的分布;为了减少冻害对寒区工程的破坏,应采取良好的保温措施.模拟结果与现有研究成果和工程经验类似.     

Strain partitioning in banded and/or anisotropic rocks: Implications for inferring tectonic regimes

Among the many concepts that have contributed to the development of structural geology in the last half-century, two are particularly important. These are: (i) the link between the symmetry of the structure, the vorticity of the associated deformation process and the tectonic regime, and (ii) the widespread partitioning of strain. However, a clear understanding of these concepts and the links between them are not always apparent in structural analyses carried out to determine the prevailing tectonic regime of an area through the use of structural symmetries and kinematic indicators. This contribution, based on field studies from Cap de Creus, experimental data and theoretical concepts, highlights some of the problems encountered when attempting to deduce the type of strain and associated regional tectonic regime from field structures. The relation between the symmetry of a structure and its associated kinematics is not unique. For example, it is demonstrated that in mechanically anisotropic materials, symmetry variations do not necessarily reflect marked vorticity variations, but rather the angular variations between the kinematic framework and the anisotropy planes. Because of widespread strain partitioning, local and general kinematics do not generally match. This mismatch is especially accentuated in rheologically heterogeneous rocks. Nevertheless, correct interpretations are possible by performing continuous multi-scale structural analyses in which the impact of strain partitioning and of the presence of material anisotropies and heterogeneities are considered.     

基于图像分割的煤岩割理CT图像各向异性特征

利用工业CT对自然煤岩样进行断层扫描观测。针对煤岩裂隙系统的多尺度、各向异性特征,应用Canny算子图像分割与方向性边缘检测技术,提取煤岩CT图像割理的总体特征、水平方向和垂直方向特征;根据特征图像计算了煤岩样的总体分形维数、孔隙度,各向异性分形维数与孔隙度及其在三维空间中的分布;讨论了分形维数与孔隙度、渗透率之间的关系,并根据煤岩样的分形维数、孔隙度对实际工程岩体的孔隙度和渗透率进行了外推计算。研究表明,煤岩样不同扫描断面的分形维数和孔隙度不同,同一煤样同一断面不同方向的分形维数与孔隙度亦不相同。利用图像分割与边缘检测对工业CT图像进行分析,可以对煤岩的各向异性分形维数与孔隙度在2D与3D空间进行精细描述。     

Fabric symmetry of low anisotropic rocks inferred from ultrasonic sounding: Implications for the geomechanical models

The geomechanical models were established based on the absence or presence of certain rock fabric elements — texture (crystallographic preferred orientation), microstructure (shape preferred orientation) and microcracks (flat voids). The proposed models include both (i) the ideal material showing random texture and structure but no microcracks, i.e. the material which is hardly to be found in nature, and (ii) the materials possessing various combinations of fabric elements that show different spatial arrangements. The mutual relationship between those parameters and seismic and geomechanical properties are discussed.Selected models were experimentally verified during laboratory experiments. These consist of measurement of P-wave velocities in 132 independent directions under several confining pressures in the range 0.1–400 MPa. From measured data 3D P-wave patterns can be constructed and the influence of microcracks and of texture and structure on the rock seismic anisotropy can be determined. The seismic anisotropy established at different levels of confining pressure can be used for the interpretation of rock fabric symmetry of rocks showing low anisotropy in macroscale and for the selection of directions in which the geomechanical test can be performed. The measured P-wave velocities were then mathematically processed by using a fitting function which reflects contribution of P-wave velocity in the mineral skeleton of an ideal sample without microcracks extrapolated to the atmospheric pressure level from high confining pressure interval (ca. 200–400 MPa) (v₀), linear compressibility of the samples (k_v), and confining pressure during which most of the cracks are closed (P₀). These parameters improve the understanding of the response of various rock fabric elements on increasing confinement and corresponding changes in elasticity.The observed seismic and geomechanical anisotropies reflect intensity of the fabric of rock-forming minerals and microcracks. The magnitude of seismic anisotropy measured at atmospheric pressure corresponds to the anisotropy of static elastic modulus and is governed by the spatial arrangement of microcracks. The magnitude of strength anisotropy (uniaxial compressive strength) correlates more likely to the seismic anisotropy determined at high confining pressure and is connected to the preferred orientations (either CPO or SPO or both) of rock-forming minerals.     

岩石中铜的测量不确定度评定

本文对火焰原子吸收法测定岩石中铜的不确定度进行了评定,分析了该方法测定过程中的不确定度来源,建立了数学模型并对不确定度加以合成、扩展,以赋予不确定度的方式给出测定结果.     

Preliminary investigation results on fabrics and related physical properties of an anisotropic gneiss

In order to evaluate the fabric-dependent anisotropy of a particular gneiss type, we assessed the quartz lattice and shape preferred orientations as well as the microcrack pattern statistics. In the rock mechanics laboratory, several strength and deformability tests on drilled rock samples were run and the seismic wave propagation properties along the rock’s principal strain axes were determined. In the mechanical tests it turned out that despite a distinct stretching lineation with initially extreme grain elongation, the rock performs for the larger part as a transversely isotropic material with the schistosity as plane of isotropy. The anisotropy in seismic wave propagation within the plane of schistosity is attributed primarily to a highly anisotropic microcrack pattern, the distinct gneissose banding and to a lower degree to the LPO of quartz.     

Determination of soil properties for plane strain condition from the triaxial tests results

Significant difference in stress–strain behavior of dense cohesionless soil has been observed between plane strain and triaxial test conditions. At present, majority of geotechnical laboratories have no plane strain testing facility. Therefore, geotechnical professionals are more dependent on the conventional triaxial test for soil properties, whereas many geotechnical structures prevail close to plane strain condition. A method has been proposed to determine soil properties for plane strain condition from the conventional triaxial tests. This method can especially be used to determine the internal friction angle and stress–strain relationship for plane strain condition from triaxial tests results. Copyright © 2015 John Wiley & Sons, Ltd.     

Engineering geological characterization of low strength anisotropic rocks in the Himalayan region for assessment of tunnel support

A detailed engineering geological assessment of low strength (6–35 MPa) anisotropic rocks at an ongoing Hydroelectric Project in the Himalayan Region has been carried out. The project (the Nathpa Jhakri Hydroelectric Project) will have one of the world's largest and longest water conducting systems, consisting of a 10.15 m diameter and 27.3 km long head race tunnel, a 942 000 m³ underground desilting complex and a 20 × 49 × 216 m powerhouse cavern in the area. Because these constructions are made in low strength metamorphosed anisotropic rocks like quartz mica schists, biotite schists and muscovite schists, it seemed necessary and worthwhile to undertake a comprehensive study of such rocks. The studies include petrographic and petrofabric analyses of the rocks, geo-mechanical properties, rock stress measurements, rock mass classification using the Q-System and data concerning joint geometry, joint roughness and joint strength. The use of mapped geological and geotechnical data along with the experimental and modelling studies have helped to better understand the behaviour of these rocks in underground openings.